Things Are Looking Brighter For Fluorescent Bulbs

NEW YORK — The incandescent light bulb, invented by Thomas Edison in 1879, was such a good idea that it has since become a symbol of inspiration, hovering over heads at the moment of discovery.

In the century since Edison`s invention, the incandescent bulb has been overtaken in many offices and businesses by the more energy-efficient fluorescent bulb. But for use in ordinary household fixtures, consumers have found no acceptable alternative to the pear-shaped incandescent, whose virtues include low cost, small size and a pleasing light complimentary to skin tones.

Recently, however, the nation`s major lighting manufacturers -- General Electric, Sylvania, which is a subsidiary of GTE, and North American Philips -- have begun to market compact fluorescent bulbs that experts say may eventually replace incandescents in many of the most frequently used household sockets.

These bulbs, which have gained wide acceptance in Europe, are an offshoot of the development of high-efficiency, rare-earth phosphors, which allow fluorescent bulbs to be made smaller as well as to emit a spectrum of light almost identical to the so-called warm hue of the standard incandescent. Phosphors are chemical compounds that convert ultraviolet light to visible light.

``The incandescent is not going to disappear,`` said Rudy Verderber, group leader for the lighting research program at the Lawrence Berkeley Laboratory. But in time, it will be replaced by compact fluorescents in fixtures that are frequently left on for long periods, such as those outdoors and in hallways, he said. These bulbs ``last longer and they are more efficient.``

Compact fluorescents have an expected lifespan of 10,000 hours, 10 times that of an ordinary incandescent. Their only drawback, Verderber said, is that ``the initial cost is greater.``

Composed of two thin tubes bridged by a connecting tube at the top, compact fluorescents carry a retail price of about $10, while an incandescent bulb can be bought in a supermarket for about 70 cents. To fit the compact fluorescent bulbs, which are pronged, into an ordinary socket, an adapter, costing another $10, is required. The adapter, which does not need to be replaced with the bulb, regulates the voltage.

John Hoffman, fluorescent product manager at the North American Philips Lighting Corp., which spearheaded the introduction of compact fluorescent bulbs in this country more than three years ago, estimated that 2 million compact fluorescent bulbs are sold in the United States annually. Compared with the almost 2 billion ordinary incandescent bulbs sold last year, the number of compact fluorescents, is ``very small,`` he said, but it is a number that is growing. ``The response to the bulbs has been very good,`` he added.

Both incandescent and fluorescent light bulbs convert electrical energy into light, but they do so in different ways.

In an incandescent bulb, current heats a tungsten filament, which glows white hot, releasing some of its energy as visible light.

In a fluorescent bulb, a stream of electrons flows between electrodes sealed in both ends of a tube containing inert gases and mercury. The current vaporizes the mercury, which produces an arc stream that gives off ultraviolet light. A coating of phosphors in the tube converts the ultraviolet light to visible, white light. This method of producing light is more efficient than filament bulbs; a 4-foot fluorescent, for example, uses half the energy and emits almost twice the light as a 100-watt incandescent.

Developing a fluorescent bulb at once small enough and bright enough for household use was made possible by the discovery in the late 1970`s of different phosphors, called rare-earth phosphors, according to Alvin Hart, manager of application engineering at GE`s lighting business group.

Unlike ordinary phosphors, which break down when brought too close to the arc stream, rare-earth phosphors, which contain rare-earth elements such as yttrium and europium, can withstand a relatively high current passing through a narrow tube.

Today`s compact fluorescents start as small as 2 1/2 inches long for a 5- watt bulb that emits the light of a 25-watt incandescent. The largest compact fluorescent is an 18-watt bulb with a built-in adapter that gives off slightly less light than a 75-watt incandescent. The bulb, about 6 1/2 inches long, is made by North American Philips.

While the initial cost of a compact fluorescent is several times higher than that of an incandescent, lighting manufacturers say that the fluorescent more than pays for itself in saved electricity costs.